Designing benzosiloles for better optoelectronic properties using DFT & TDDFT approaches

Abstract

Like siloles, benzosiloles have low lying LUMOs due to σ*-π* conjugation between Si and the butadiene moiety but are more amenable for structural tuning. In total, 27 benzosiloles, 12 of them already synthesized and another 15 newly reported here, have been investigated using DFT and TDDFT calculations with an aim to check their suitability for optoelectronic applications. Our results show that all these molecules have excellent π-conjugation throughout. Frontier molecular orbital analysis gives an estimate of the band gap of these benzosilole derivatives and further reveals that the LUMOs are highly localized on the benzosilole moiety whereas HOMOs are localized on both the benzosilole moiety and the substituents. TDDFT calculations have been performed to understand the absorption properties in gas and solvent phases. PCM calculations show that solvation has a minimum effect on absorption maxima. Among the different functionals, PBE0 was found to perform well compared to other functionals and the computed absorption spectra are in good agreement with experiments. Among the designed candidates, styryl substituted benzosiloles are the most promising, showing higher wavelength of absorption and would make better OLED materials. NBO and AIM analysis provide evidence for complete delocalization in these systems. It is interesting to note that eleven out of the fifteen newly designed candidates have lower band gaps than the best known benzosilole derivatives synthesized so far.